Many body fluid processing protocols, particularly those involving diagnostic testing, include determining whether a particular substance, e.g., a target analyte, is present in the body fluid. Many of these tests rely on colorimetric or spectrophotometric evaluation of a reaction of a fluid component with one or more specific reagents. Other tests include evaluating changes in pH or electrical conductance to determine the presence of the analyte. However, these tests may yield less than optimum results, since, for example, the fluid may fail to efficiently wet the test device, and/or other substances present in the body fluid may interfere with the particular substance to be analyzed and/or cause difficulties in interpreting the test results.
Illustratively, when the body fluid to be tested is blood, the red color due to the presence of red blood cells and/or the hemoglobin released by hemolyzed red cells may interfere with diagnostic tests which employ color change as part of their procedure. Accordingly, many body fluid testing protocols include separating one or more components from the body fluid before testing. For example, plasma or serum may be separated from blood before subjecting the plasma or serum to analysis, so that cellular material, e.g., red and/or white blood cells, will not interfere with the test results.
One technique for separating plasma or serum from other blood components such as red blood cells includes obtaining blood, e.g., from a finger prick, and placing the blood on a blood test strip. The test strip, which includes at least one porous element, allows blood to flow into the strip, and a portion of plasma to be separated from the cells contained in the blood sample. Some test strips may include a plurality of porous elements that allow the passage of plasma or serum therethrough, wherein at least one element may include one or more reagents that react with the analyte so that the presence of the analyte in the plasma or serum may be determined.
However, the prior art test strips suffer from a number of drawbacks. A particular drawback is a lack of product reproducibility, as the strips are difficult to produce with a sufficient degree of uniformity. For example, some strips are insufficiently uniform to provide for efficient and/or reproducible plasma separation. Illustratively, some strips include fibrous webs having a stripy appearance resulting from a lack of uniform fiber distribution, e.g., ridges of fibers. Since the fiber distribution is not uniform, some test strips include multiple layers of webs, e.g., about 10 layers or more, to provide for separation. In view of the number of layers, such devices may require a relatively large amount of blood to provide sufficient plasma for a diagnostic test.
Other devices, with or without fibrous media, fail to provide a sufficiently large plasma front ahead of the front of cellular material to allow testing of the plasma without interference from the cellular material, consequently, the failure of these devices to efficiently separate plasma may require the use of a relatively large blood sample to assure that sufficient plasma is available to be tested.
Additionally, since some devices include one or more reagents preplaced in one or more areas of the device, a lack of product reproducibility from one device to another may lead to the failure of the plasma to contact the reagent(s) in a particular location and/or to contact the reagent(s) for a sufficient amount of time. For example, since some preplaced reagents are soluble, devices that allow the plasma to pass through too quickly may fail to allow the plasma to dissolve the reagent, leading to an inaccurate test result. Accordingly, due to a lack of uniformity, two devices may provide different test results for the same patient using consecutive drops of blood, and it may be difficult to determine which, if either, of the devices have provided an accurate result.
Furthermore, particularly for some of those strips including at least two porous elements secured to each other, it may be awkward and/or difficult to bond the elements together. Not only is the bond generally weak, but the elements tend to be undesirably compressed when they are pressed together to form the bond, which in turn decreases the effectiveness of plasma separation. Moreover, the permeability of the bond, or the area near the bond, may be adversely affected.
Accordingly, there is an ongoing need in the art for body fluid processing devices and methods for using them that provide for efficient separation of at least one desired component of the body fluid in sufficient amounts for analysis. Such processing devices are preferred to be easy to use, whether it is by patients, or by medical personnel such as physicians, nurses, or lab technicians. Moreover, the devices should be sufficiently uniform so that the test results are accurate and reproducible.
Additionally, the devices are preferred to allow efficient separation of plasma from blood without removing a significant proportion of the substance(s) or material(s) in the plasma to be analyzed or determined, e.g., glucose, cholesterol, lipids, serum enzymes, nucleic acids, viruses, bacteria, and/or coagulation factors, to name but a few.
The present invention provides for ameliorating at least some of the disadvantages of the prior art test strips and methods for using them. The present invention can also be used for protocols involving the processing of non-biological fluids. These and other advantages of the present invention will be apparent from the description as set forth below.